Semiconductor film, semiconductor device, and method of manufacturing the same

ABSTRACT

By adding a novel improvement to the technique disclosed in JP 8-78329 A, a manufacturing method in which film characteristics of a semiconductor film having a crystalline structure are improved is provided. In addition, a TFT having superior TFT characteristics, such as field effect mobility, which uses the semiconductor film as an active layer, and a method of manufacturing the TFT, are also provided. A metallic element which promotes the crystallization of silicon is added to a semiconductor film having an amorphous structure and an oxygen concentration within the film of less than 5×10 18 /cm 3 . The semiconductor film having an amorphous structure is then heat-treated, forming a semiconductor film having a crystalline structure. Subsequently, an oxide film on the surface is removed. Oxygen is introduced to the semiconductor film having a crystalline structure, and processing is performed such that the concentration of oxygen within the film is from 5×10 18 /cm 3  to 1×10 21 /cm 3 . After removing an oxide film on the surface of the semiconductor film, the semiconductor film surface is leveled by irradiating laser light under an inert gas atmosphere or in a vacuum.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the invention.

[0002] The present invention relates to a semiconductor device having acircuit composed of thin film transistors (hereinafter, referred to asTFTs) and a method of manufacturing the semiconductor device. Forexample, the present invention relates to an electro-optical devicetypified by a liquid crystal display panel and an electronic equipmentmounted with the electro-optical device as a component.

[0003] Note that the term semiconductor device in this specificationindicates devices in general capable of functioning with the use ofsemiconductor characteristics, and electro-optical devices,semiconductor circuits and electronic equipment are all included in thecategory of the semiconductor device.

[0004] 2. Description of the Related Art

[0005] In recent years, a technology of constituting a thin filmtransistor (TFT) by using a semiconductor thin film (with a thickness ofapproximately several to several hundred of nm) formed on a substratehaving an insulating surface has attracted attention. The thin filmtransistor is widely applied to an electronic device such as an IC or anelectro-optical device, and needs to be developed promptly as, inparticular, a switching element of an image display device.

[0006] An active matrix liquid crystal module is known as a typicalexample of the thin film transistors. Particularly, a TFT having asilicon film having a crystalline structure (typically, polysiliconfilm) as an active layer (hereafter, referred to as polysilicon TFT) hashigh filed-effect mobility compare to a TFT having a silicon film havinga amorphous structure (typically, amorphous silicon film), and thus suchTFTs are multiused recently.

[0007] Although there are various technologies of obtaining the siliconfilm having crystalline structure, especially, a technology given inJapanese Unexamined Patent Publication No. Hei. 8-78329 official report,in which the metallic elements (typically nickel) promotingcrystallization to an amorphous silicon film are added alternatively,thereby performing a heat treatment to form the crystalline silicon filmwhich spreads with an addition region as the starting point. Since thesize of the crystal grain obtained thereof is very large compared withother technologies, and the field effect mobility is high, variouscircuits equipped with various functions can be formed thereby. Forexample, in case of using the technology of the above-mentioned officialreport, to a liquid crystal module carried in a liquid crystal displaydevice, drive circuits for controlling pixel portions, such as pixelportions which perform an image display for every functional block, ashift register circuit based on a CMOS circuit, a level shifter circuit,a buffer circuit, and a sampling circuit, and the like can form on onesubstrate.

[0008] Moreover, the above-mentioned official report technology canlower approximately 50-100° C. crystallization temperature of anamorphous silicon film by the action of metallic elements compared to amethod without using metallic elements, thereby a glass substrate can beused without any problems occurring in process. Moreover, required timein the crystallization of the above-mentioned official report technologycan be reduced to ⅕-{fraction (1/10)} compared to the method withoutusing metallic elements, thereby the above-mentioned official reporttechnology is also excellent in productivity.

SUMMARY OF THE INVENTION

[0009] A new further improvement is added to the technology of theabove-mentioned official report, the manufacturing method of improvingthe film characteristic of a semiconductor film having a crystallinestructure, and TFTs in which such a semiconductor film used as an activelayer, excellent in the TFTs characteristics, such as the field effectmobility, are offered.

[0010] Considering the results of many experiments performed from a widevariety of fields in order to resolve the aforementioned variousproblems has lead to the present invention. When heat treatment isperformed for crystallization, it is preferable to reduce theconcentration of oxygen, which impedes crystallization, within asemiconductor film having an amorphous structure to which a metallicelement is added for promoting crystallization, to a value as small aspossible, specifically to less than 5×10¹⁸/cm³. It was discovered thatthe above problems can be resolved, in particular field effect mobilitycan be increased, by performing the introduction of oxygen into the filmafter performing heat treatment.

[0011] The oxygen concentration within the film may be set from5×10¹⁸/cm³ to 1×10²¹/cm³ by irradiating laser light under an inert gasatmosphere, or in a vacuum, after oxidizing a surface of thesemiconductor having a crystalline structure by using ozone water as aprocessing of introducing oxygen into the semiconductor film having acrystalline structure.

[0012] Alternatively, the oxygen concentration within the film may beset from 5×10¹⁸/cm³ to 1×10²¹/cm³ by irradiating laser light under anatmosphere containing oxygen or water molecules as another process ofintroducing oxygen into the semiconductor film having a crystallinestructure.

[0013] In addition, the oxygen concentration within the filmmay be setfrom 5×10¹⁸/cm³ to 1×10²¹/cm³ by irradiating laser light under an inertgas atmosphere, or in a vacuum, after performing oxidation under anatmosphere containing oxygen or water molecules by using an electricfurnace or the like. Further, the oxygen concentration within the filmmay be set from 5×10¹⁸/cm³ to 1×10²¹/cm³ by irradiating laser lightunder an inert gas atmosphere, or in a vacuum, after adding oxygen byion doping or ion implantation so that the oxygen concentration withinthe semiconductor film becomes 5×10¹⁸/cm³ to 1×10¹⁸/cm³. Furthermore,the semiconductor film is melted instantaneously from the surface, afterwhich the melted semiconductor film is cooled and solidified from thesubstrate side because of thermal conduction to the substrate, for casesin which laser light is irradiated to the semiconductor film.Recrystallization takes place during the solidification process, and thesemiconductor film becomes the one having a crystalline structure with alarge grain size, but volumetric expansion develops due to the temporarymelting, and unevenness referred to as ridges forms in thesemiconductor-surface. In particular, the surface on which the ridgesform becomes an interface with a gate insulating film for top gate TFTs,and therefore the element characteristics vary greatly.

[0014] In addition to the above processes, the oxide film on thesemiconductor film surface is removed after laser light irradiationaccording to the present invention, and in addition, laser light is thenirradiated under an inert gas atmosphere, or in a vacuum to level thesurface of the semiconductor film having a crystalline structure.

[0015] Note that, differing from a technique for performingcrystallization of the film having an amorphous structure by a firstlaser light and leveling by using a second laser light (JP 2001-60551A), the present invention concerns irradiating the first laser light tothe semiconductor film having a crystalline structure. Further, thepresent invention is the one in which a metallic element for promotingcrystallization is added, a semiconductor film having a crystallinestructure is formed, and levelness is additionally increased by theaddition of the metallic element.

[0016] A first aspect of the present invention disclosed by thisspecification relates to a method of manufacturing a semiconductordevice, including:

[0017] a first step of forming a semiconductor film having an amorphousstructure on an insulating surface;

[0018] a second step of adding a metallic element to the semiconductorfilm having an amorphous structure;

[0019] a third step of heat-treating the semiconductor film having anamorphous structure to form a semiconductor film having a crystallinestructure, and then removing an oxide film from the crystallinesemiconductor film surface;

[0020] a fourth step of introducing oxygen into the semiconductor filmhaving a crystalline structure to make an oxygen concentration withinthe film from 5×10¹⁸/cm³ to 1×10²¹/cm³;

[0021] a fifth step of removing an oxide film on the surface of thesemiconductor film having a crystalline structure; and

[0022] a sixth step of irradiating laser light under an inert gasatmosphere or in a vacuum to level the surface of the semiconductor filmhaving a crystalline structure.

[0023] Further, although the oxide film is formed on the surface whenheat-treating the semiconductor film having an amorphous structure, theprocess of introducing oxygen may also be performed without removing theoxide film. A second aspect of the present invention relates to anothermethod of manufacturing a semiconductor device, including:

[0024] a first step of forming a semiconductor film having an amorphousstructure on an insulating surface;

[0025] a second step of adding a metallic element to the semiconductorfilm having an amorphous structure;

[0026] a third step of heat-treating the semiconductor film having anamorphous structure to form a semiconductor film having a crystallinestructure;

[0027] a fourth step of introducing oxygen into the semiconductor filmhaving a crystalline structure to make the oxygen concentration withinthe film from 5×10¹⁸/cm³ to 1×10²¹/cm³;

[0028] a fifth step of removing an oxide film on the surface of thesemiconductor film having a crystalline structure; and

[0029] a sixth step of irradiating laser light under an inert gasatmosphere or in a vacuum to level the surface of the semiconductor filmhaving a crystalline structure.

[0030] Furthermore, in the present invention, although the metallicelement for promoting crystallization (typically Ni) is added onto thesemiconductor film having an amorphous structure so as to causecrystallization, it is preferable that the metallic element forpromoting crystallization be removed by a gettering technique or thelike after crystallization. A third aspect of the present inventionrelates to another method of manufacturing a semiconductor device,including:

[0031] a first step of forming a semiconductor film having an amorphousstructure on an insulating surface;

[0032] a second step of adding a metallic element to the semiconductorfilm having an amorphous structure;

[0033] a third step of heat-treating the semiconductor film having anamorphous structure to form a semiconductor film having a crystallinestructure, and then removing an oxide film from the crystallinesemiconductor film surface;

[0034] a fourth step of introducing oxygen into the semiconductor filmhaving a crystalline structure to make the oxygen concentration withinthe film from 5×10¹⁸/cm³ to 1×10²¹/cm³;

[0035] a fifth step of removing an oxide film on the surface of thesemiconductor film having a crystalline structure;

[0036] a sixth step of irradiating laser light under an inert gasatmosphere or in a vacuum to level the surface of the semiconductor filmhaving a crystalline structure; and

[0037] a seventh step of gettering the metallic element to remove themetallic element from, or reduce the concentration of the metallicelement within, the semiconductor film having a crystalline structure.

[0038] Further, in each of the aforementioned aspects of the invention,the energy density of the laser light used in performing the sixth stepis set to 430 to 560 mJ/cm², and the laser light irradiation performedby the fourth step uses laser light having an energy density that islower by 30 to 60 mJ/cm² than that of the laser light used by the sixthstep (between 400 and 500 mJ/cm²).

[0039] Further, semiconductor films having the crystalline structureobtained by the above manufacturing method are included in the presentinvention. An aspect of a semiconductor device containing thesemiconductor film having a crystalline structure of the presentinvention includes a TFT having:

[0040] a semiconductor layer having a channel formation region, a drainregion, and a source region;

[0041] a gate insulating film; and

[0042] a gate electrode,

[0043] in which:

[0044] a metallic element is contained within the semiconductor layer ata concentration of 1×10¹⁶/cm³ to 5×10¹⁸/cm³; and

[0045] average surface roughness (Ra value) of a surface of thesemiconductor layer is equal to or less than 2 nm as obtained by AFM(atomic force microscopy).

[0046] Note that the metallic element in the above aspect is a metallicelement for promoting crystallization of silicon, and is one element, ora plurality of elements, selected from the group consisting of Fe, Ni,Co, Ru, Rh, Pd, Os, Ir, Pt, Cu, and Au.

[0047] Further, extremely unique data on a state of the film surface isalso obtained for the semiconductor film having a crystalline structureof the present invention, at the same time as data is obtained onsuperior levelness, by using AFM (atomic force microscopy). For cases inwhich a metallic element which promotes crystallization is not used, atortoiseshell pattern is formed surrounded by ridges (portions in whichmicroscopic convex portions extend continuously). An irregular meshpattern in which several regions exist, divided by ridges extending inmany directions as shown in FIG. 3, can be observed, however, as thesurface state of the semiconductor film having a crystalline structureof the present invention in which crystallization is performed using ametallic-element which promotes crystallization. Regions sandwiched bythe ridges (level portions and concave portions) correspond well to anaggregation of crystal grains having the same crystal orientation (alsoreferred to as domains).

[0048] The semiconductor film of the present invention has an irregularmesh pattern in the semiconductor film surface, as shown in FIG. 3.Ridges having convex portions extending out in a ridge shape diverge inmany directions, and there is at least one pathway not obstructed by theridges between two arbitrary points in a region containing levelportions and concave portions sandwiched irregularly by the ridges. Notethat the ridges are formed by performing laser light irradiation aplurality of times.

[0049] Further, the ridges having convex portions that extend out in aridge shape with forming an irregular mesh pattern are formed inlocations that nearly correspond to individual domain boundaries. Thefact that the individual domain boundaries and the ridges nearlycorrespond can be verified by a method referred t-o as unique grainmapping (in which an electron beam is scanned over a sample, and fromthe crystal orientations found at each point, regions are classified inwhich crystal orientations have an angular shift less than 15° betweentwo adjacent points at the respective measurement points). Here, SEMobservation photograph and electron backscatter diffraction pattern(EBSP) are used in the analysis in the same region. That is, in additionto the fact that there is at least one pathway not obstructed by theridges between two arbitrary points in a region containing levelportions and concave portions sandwiched irregularly by the ridges,there is a pathway between two arbitrary points in a region sandwichedby domain boundaries in which the shift between adjacent points incrystal orientations is less than 15°. This can be expected to be afactor in obtaining a semiconductor film having superior electricalcharacteristics, in particular, superior field effect mobility.

[0050] Further, the above surface state and crystal orientationcharacteristics are characteristic of the present invention and cannotbe obtained by another method. The characteristic can first be seenafter adding a metallic element for promoting crystallization (typicallynickel), crystallizing by performing heat treatment, and in addition,removing an oxide film on the semiconductor film surface afterperforming irradiation of a first laser light, and leveling the surfaceof the semiconductor film having a crystalline structure by irradiatinglaser light under an inert gas atmosphere or in a vacuum.

[0051] Also, in the aforementioned semiconductor film, a metallicelement is contained therein at a concentration of 1×10¹⁶/cm³ to5×10¹⁸/cm³. Furthermore, the semiconductor film is level, having anaverage surface roughness (Ra value) equal to or less than 2 nm.

[0052] Further, a semiconductor device having superior electricalcharacteristics can be obtained by using the semiconductor film as aportion of the semiconductor device, for example as an active layer of aTFT.

[0053] An aspect of a semiconductor device of the present inventionincludes a TFT having:

[0054] a semiconductor layer having a channel formation region, a drainregion, and a source region;

[0055] a gate insulating film; and

[0056] a gate electrode,

[0057] in which:

[0058] a surface of the semiconductor layer has an irregular meshpattern;

[0059] ridges having convex portions that extend out in a ridge shapediverge in many directions; and

[0060] at least one pathway that is not obstructed by the ridges isprovided between two arbitrary points in a region containing a levelportion and a concave portion sandwiched irregularly by the ridges. Ametallic element is contained within the aforementioned semiconductorlayer at a concentration of 1×10¹⁶/cm³ to 5×10¹⁸/cm³. Furthermore, thesemiconductor layer is level, having an average surface roughness (Ravalue) equal to or less than 2 nm.

[0061] The crystalline structure for cases in which crystallization isperformed by a conventional solid phase growth method becomes a twinstructure, and a semiconductor film contains a large number of twindefects within the crystal grains. In contrast, a plurality of rod shapecrystal grain aggregates (domains) are formed in a semiconductor filmobtained by the present invention, and all of the crystal grains of acertain crystal grain aggregate (domain) can be considered to have thesame crystal orientation. The size of the crystal grain aggregate(domain) is equal to or greater than approximately 1 μM, with the largeones having a size of several tens of micrometers.

[0062] Further, the number of defects contained in the grain boundarieswithin one domain (unbonded hands of silicon) is extremely small, andthe electrical barrier is small, compared to the grain boundariesobtained by the conventional solid phase growth methods or the like.That is, the interior of one domain is approximately close to a singlecrystal, and it is thought that the film characteristics will becomemore superior, the larger the domain size becomes.

[0063] The term adjacent crystal aggregates (domains) refers toaggregates having different orientations with a boundary (portion inwhich a microscopic convex portion extends continuously) between theaggregates. Similarly, the surface state can also be observed by usingSEM observation.

[0064] Note that FIG. 3 is a diagram showing AFM observation afterperforming crystallization by using heat treatment, irradiating laserlight under an atmosphere containing oxygen as a process of introducingoxygen into the film, removing an oxide film on the surface, and thenperforming leveling by irradiating laser light under a nitrogenatmosphere. On the other hand, FIG. 2 is a diagram showing AFMobservation after performing crystallization by using heat treatment,and irradiating laser light under an atmosphere containing oxygen as aprocess of introducing oxygen into the film, but it is difficult to seedomain boundaries. As described above, individual domain boundaries canbe confirmed by AFM and SEM by removing an oxide film on the surface,and then irradiating laser light under an inert atmosphere or in avacuum. Note that, except for making the film surface flat and allowingindividual domains to be clearly visualized, the irradiation of laserlight under an inert atmosphere or in a vacuum imparts almost no changesto the semiconductor film or to the crystalline state. That is, the sizeof the domains obtained by the present invention is determined by theprocesses performed before irradiating the laser light under an inertatmosphere or in a vacuum (such as processes for forming a semiconductorfilm having an amorphous structure, heat treatment for crystallization,and processes for introducing oxygen).

BRIEF DESCRIPTION OF THE DRAWINGS

[0065] In the accompanying drawings:

[0066]FIGS. 1A to 1F are views of a manufacturing process of the presentinvention;

[0067]FIG. 2 is an observation view by AFM;

[0068]FIG. 3 is an observation view by AFM;

[0069]FIGS. 4A to 4D are views of a manufacturing process of an activematrix substrate;

[0070]FIGS. 5A to 5C are views of a manufacturing process of an activematrix substrate;

[0071]FIG. 6 is a view of an active matrix substrate;

[0072]FIG. 7 is a view of an outer appearance of an AM-LCD; (Embodiment2)

[0073]FIG. 8 is a view of an example of a sectional view of a liquidcrystal display device; (Embodiment 3)

[0074]FIGS. 9A to 9F show examples of electronic equipment;

[0075]FIGS. 10A to 10D show examples of electronic equipment;

[0076]FIGS. 11A to 11C show examples of electronic equipment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0077] Embodiment Mode

[0078] Embodiment Mode of the Present Invention will be Explained.

[0079] An example of manufacturing a semiconductor film having acrystalline structure of the present invention is shown in FIGS. 1A to1F.

[0080] A semiconductor film 11 having an amorphous structure is firstformed on a substrate 10 (See FIG. 1A). Glass substrates, quartzsubstrates, and silicon substrates may be used as the substrate 10, asmay metallic substrates and stainless steel substrates having aninsulating film formed on the surface thereof. Further, plasticsubstrates having thermal resistance capable of withstanding processingtemperatures may also be used.

[0081] Note that a base insulating film may be formed if necessary toprevent impurities from the substrate 10 from diffusing, and thesemiconductor film having an amorphous structure may be formed on thebase insulating film to prepare the base insulating film. The base filmmay be formed from an insulating film such as a silicon oxide film, asilicon nitride film, or a silicon oxynitride film. Note that it ispreferable to form the base insulating film for cases in which a glasssubstrate is used.

[0082] Further, the semiconductor film 11 having an amorphous structureuses a semiconductor material having silicon as its main constituent. Anamorphous silicon film, an amorphous silicon germanium film, or the likeis typically applied, and formed to a thickness of 10 to 100 nm by usingplasma CVD. Note that it is very important that the concentration ofoxygen contained in the semiconductor film 11 having an amorphousstructure after film formation be from 1×10¹⁸/cm³ to 4×10¹⁸/cm³,approximately 3×10⁸/cm³ (by SIMS measurement).

[0083] Crystallization is performed next using a technique disclosed inJP 8-78329 A as a method of crystallizing the semiconductor film havingan amorphous structure. The technique recorded in JP 8-78329 is one inwhich a metallic element which promotes crystallization is selectivelyadded to an amorphous silicon film, and a semiconductor film having acrystalline structure is formed, the crystalline structure spreading outwith the regions to which the metallic element is added acting ascrystallization origins. First, a nickel acetate solution containing ametallic element (nickel is used here) having a catalytic action forpromoting crystallization at 1 to 100 ppm by weight is applied by aspinner, forming a nickel containing layer 12. Means of forming anextremely thin film by sputtering, evaporation, or plasma processing mayalso be used as other means instead of forming the nickel containinglayer 12 by an application method. Further, although the solution isapplied over the entire surface with the example shown here, the nickelcontaining layer 12 may also be formed selectively by using a mask. (SeeFIG. 1B.)

[0084] The heat treatment is performed next, thus performingcrystallization (See FIG. 1C). In this case, silicides are formed inportions of the semiconductor film contacting the metallic element thatpromotes crystallization of the semiconductor, and crystallizationproceeds with the silicides as nuclei. A semiconductor film 13 having acrystalline structure is thus formed. Note that the concentration ofoxygen contained within the semiconductor film 13 nearly does not changebefore and after crystallization by heat treatment, and it is preferablethat this concentration be less than 5×10¹⁸/cm³. After performing heattreatment for dehydrogenation (at 450° C. for 1 hour), heat treatment isthen performed (at 550° C. to 650° C. for 4 to 24 hours) forcrystallization. Further, for cases of performing crystallization by theexposure to strong light, it is possible to use infrared light, visiblelight, ultraviolet light, or a combination of these. Typically, lightemitted from a halogen lamp, a metal halide lamp, a xenon arc lamp, acarbon arc lamp, a high voltage sodium lamp, or a high voltage mercurylamp is used. Heat treatment may be performed by turning on the lamplight source for 1 to 60 seconds, preferably for 30 to 60 seconds, andrepeating this between one and 10 times, so that the semiconductor filmis instantaneously heated to a temperature on the order of 600 to 1000°C. Note that, when necessary, heat treatment for driving out hydrogencontained within the semiconductor film having an amorphous structuremay also be performed before the exposure to strong light. Further,crystallization may also be performed by using heat treatment and stronglight exposure at the same time. When considering productivity, it ispreferable to perform crystallization in a short amount of time byperforming exposure to strong light.

[0085] The metallic element (nickel here) remains in the semiconductorfilm 13 having a crystalline structure thus obtained. Even if themetallic element is not distributed uniformly within the film, itremains at an average concentration that exceeds 1×10¹⁹/cm³. It is ofcourse possible to form all types of semiconductor elements, such asTFTs, in this state, but the metallic element may also be removed usinga known gettering method.

[0086] Note that, although not shown in the figures, a thin oxide film(including a natural oxide film) is formed on the semiconductor film 13due to the above heat treatment.

[0087] A process of introducing oxygen into the film is performed nextafter removing the oxide film on the semiconductor film surface by usinghydrofluoric acid or the like. (See FIG. 1D.)

[0088] As a method of introducing oxygen into the film, an oxide film(not shown in the figures) may be formed on the surface, after whichlaser light may be irradiated under an inert gas atmosphere or in avacuum, thus setting the oxygen concentration with a semiconductor film14 a having a crystalline structure from 5×10¹⁸/cm³ to 10×10²¹/cm³,preferably greater than 2×10¹⁹/cm³. The oxide film may typically beformed on the surface by using ozone water. Further, ozone may begenerated by irradiating ultraviolet light under an oxygen atmosphere,thus oxidizing the surface of the semiconductor film, as another methodof forming the oxide film. In addition, an oxide film on the order of 1to 10 nm may also be deposited by using plasma CVD, sputtering,evaporation, or the like as another method of forming the oxide film.

[0089] Alternatively, the oxygen concentration within the film may beset from 5×10¹⁸/cm³ to 1×10²¹/cm³ by irradiating laser light under anatmosphere containing oxygen or water molecules as another process ofintroducing oxygen into the semiconductor film.

[0090] Alternatively, oxygen may also be added by ion doping or ionimplantation such that the concentration of the oxygen within thesemiconductor film is from 5×10¹⁸/cm³ to 1×10²¹/cm³, after which laserlight irradiation is performed under an inert gas atmosphere or in avacuum, thus setting the oxygen concentration within the film to5×10¹⁸/cm³ to 1×10²¹/cm³, as another process for introducing oxygen intothe semiconductor film. The concentration of oxygen within the film canbe freely set provided that ion doping or ion implantation is used, anddamage imparted to the film during the introduction may be repairedlater by the laser light.

[0091] It is necessary that as little oxygen as possible is containedwithin the film when crystallizing the semiconductor film having anamorphous structure, but good crystals easily form when there is a lotof oxygen present during laser irradiation, and when using thecrystallized film as an active layer of a TFT, high values for the TFTelectrical characteristics, such as electric field effect mobility, areseen.

[0092] A diagram in which observation by AFM is performed afterirradiating laser light (452.5 mJ/cm²) under an atmosphere containingoxygen is shown in FIG. 2. With AFM, a 4 μm by 4 μm region in which Rais 10.49 nm, Rms is 12.97 nm, and the P-V value is 91.32 nm is shown. Anextremely large roughness is formed by the laser light irradiation,considering that the film thickness of the semiconductor film beforelaser light irradiation is approximately 50 nm.

[0093] Further, the oxide film on the surface is removed before theprocess of introducing oxygen, but laser light irradiation or the oxygenintroducing process may also be performed without removing the oxidefilm.

[0094] A thin oxide film (not shown in the figures here) is formed dueto a minute amount of oxygen in a nitrogen atmosphere or in a vacuumwhen irradiating laser light during the process of introducing oxygen.Furthermore, a natural oxide film (not shown in the figures here) isformed if there is contact with the atmosphere, even for cases in whichlaser light is not irradiated.

[0095] The oxide film on the semiconductor film surface (including thenatural oxide film) is next removed by diluted hydrofluoric acid or thelike, and a semiconductor film 14 b having a crystalline structure isobtained. (See FIG. 1E.)

[0096] Laser light (430 to 560 mJ/cm²) is then irradiated to thesemiconductor film l4 b having a crystalline structure under a nitrogenatmosphere or in a vacuum (See FIG. 1F). For cases in which laser lightis irradiated in the previous process, which is the process ofintroducing oxygen, ridges are reduced, that is, the ridges are leveled,if the energy density used in the process of introducing oxygen is setto be less than that of the laser light used in FIG. 1F by 30 to 60mJ/cm² (between 400 and 500 mJ/cm²). The value of Ra in the leveledsemiconductor film surface can thus be made equal to or less than 2 nm,the value of Rms can be made equal to or less than 2 nm, and the P-Vvalue of the unevenness can be made equal to or less than 50 nm.

[0097] A diagram in which observation by AFM is performed afterirradiating laser light (501 mJ/cm²) under an atmosphere containingnitrogen is shown in FIG. 3. With AFM as shown in FIG. 3, data on a 4 μmby 4 μm region in which Ra is 2.137 nm, Rms is 2.613 nm, and the P-Vvalue is 20.23 nm is shown.

[0098] Further, experimental results are shown in Table 1 for thesurface roughness (P-V value, Ra, and Rms) of semiconductor filmsmeasured by AFM after a first laser light irradiation, and after asecond laser light irradiation, respectively. TABLE 1 AFM measurementP-V value (nm) Ra value (nm) Rms (nm) region (m) 4 × 4 50 × 50 4 × 4 50× 50 4 × 4 50 × 50 After first 91.32 102.38 10.49 8.32 12.97 10.21 laserirradiation After second 20.23 36.45 2.14 1.29 2.61 1.73 laserirradiation

[0099] Note that, in Table 1, data on a 50 μm by 50 μm region in whichRa is 1.29 nm, Rms is 1.73 nm, and the P-V value is 36.45 nm is shown.

[0100] A number of rod shape crystal grain aggregates (domains) areformed in a semiconductor film 15 having a crystalline structure thusobtained. All of the crystal grains in a certain crystal grain aggregate(domain) are considered to have the same crystal orientation, and thesize of the aggregate of crystal grains (domain) is equal to or greaterthan approximately 1 μm, with large aggregates having a size of severaltens of micrometers. A TFT having superior TFT characteristics, such asfield effect mobility, can be obtained when using the semiconductor film15 having this crystalline structure as an active layer.

[0101] Note that the term “active layer” as used in this specificationindicates a semiconductor layer in a TFT having at minimum a channelformation region, a source region, and a drain region.

[0102] Further, for comparison, experimental results are shown in Table2 for the surface roughness (P-V value, Ra, and Rms) of semiconductorfilms similarly measured by AFM after a first laser light irradiation,and after a second laser light irradiation, respectively, followingcrystallization by performing heat treatment without the addition of ametallic element. TABLE 2 AFM measurement P-V value (nm) Ra value (nm)Rms (nm) region (m) 4 × 4 50 × 50 4 × 4 50 × 50 4 × 4 50 × 50 Afterfirst 79.59 81.12 11.09 8.64 13.36 10.38 laser irradiation After second30.78 110.65 2.92 1.74 3.57 2.28 laser irradiation

[0103] From Table 1 and Table 2, it can be seen that superior levelnesscan be obtained after laser light irradiation when crystallization isperformed after the addition of a metallic element. In particular,extremely good levelness having a P-V value of 20.23 nm, an Ra of 1.29nm, and an Rms or 1.73 nm is obtained after the second laser lightirradiation. Note that measurement were performed using measurementregions of 4 μm by 4 μm, and 50 μm by 50 μm. However, the value of P-Vafter the second laser irradiation in the 50 μm by 50 μm region in Table2 is an anomaly, and cannot be seen as a reliable value.

[0104] Further, although it is stated in JP 2001-60551 A that asemiconductor film is leveled by irradiating a second laser light afterperforming crystallization using a first laser light, there is nomention of increasing levelness by adding a metallic element as above.The present invention is a completely novel invention.

[0105] A more detailed explanation of the present invention having theaforementioned structure is given below using embodiments.

[0106] Embodiments

[0107] Embodiment 1

[0108] An example of the present invention is described with referenceto FIGS. 4A to 4D, FIGS. 5A to 5C and FIG. 6. Here, a method ofsimultaneously manufacturing a pixel portion and TFTs (n-channel TFTsand a p-channel TFT) of a driver circuit provided in the periphery ofthe pixel portion on the same substrate is described in detail.

[0109] First, a base insulating film 101 is formed on a substrate 100,and a first semiconductor film having a crystalline structure isobtained in accordance with the aforementioned Embodiment Modes. Then,the semiconductor film is etched to have a desired shape to formsemiconductor layers 102 to 106 separated from one another in an islandshape.

[0110] A glass substrate (#1737) is used as the substrate 100. For thebase insulating film 101, a silicon oxynitride film 101 a formed fromSiH₄, NH₃, and N₂O as material gases (composition ratio: Si=32%, 0=27%,N=24%, H=17%) is formed with a thickness of 50 nm (preferably 10 to 200nm) and, at a film deposition temperature of 400° C. by using plasmaCVD. Then, after the surface is cleaned with ozone water, an oxide filmon the surface is removed by means of dilute hydrofluoric acid (dilutionwith 1/100). Next, a silicon hydride oxynitride film 101 b formed fromSiH₄ and N₂O as material gases (composition ratio: Si=32%, 0=59%, N=7%,H=2%) is formed thereon with a thickness of 100 nm (preferably 50 to 200nm) and at a film deposition temperature of 400° C. by using plasma CVDto thereby form a lamination. Further, without exposure to anatmosphere, a semiconductor film having an amorphous structure (in thiscase, amorphous silicon film) is formed to have a thickness of 54 nm(preferably 25 to 80 nm) with SiH₄ as a film deposition gas and at afilm deposition temperature of 300° C. by using plasma CVD.

[0111] Note that it is preferable to have the oxygen concentration of asemiconductor film having an amorphous structure in a range of 1×10¹⁸ to4×10¹⁸/cm³.

[0112] In this embodiment, the base film 101 is shown in a form of atwo-layer structure, but a single layer of the insulating film or astructure in which two or more layers thereof are laminated may beadopted. Further, there is no limitation on the material of thesemiconductor film. However, the semiconductor film may be preferablyformed of silicon or silicon germanium (Si_(X)Ge_(1-X) (X=0.0001 to0.02)) alloy by using a known means (sputtering, LPCVD, plasma CVD, orthe like). Further, a plasma CVD apparatus may be a single wafer typeone or a batch type one. In addition, the base insulating film and thesemiconductor film may be continuously formed in the same film formationchamber without exposure to an atmosphere.

[0113] Subsequently, after the surface of the semiconductor film havingan amorphous structure is cleaned, an extremely thin oxide film with athickness of about 2 nm is formed from ozone water on the surface.

[0114] In order to control a threshold value of a TFT, doping (alsocalled channel doping) of a minute amount of impurity element (boron orphosphorous) can be performed. In case of performing doping, forexample, an ion doping method is used in which diborane (B₂H₆) isplasma-excited without mass-separation, and boron is added to theamorphous silicon film under the doping conditions: an accelerationvoltage of 15 kV; a gas flow rate of diborane diluted to 1% withhydrogen of 30 sccm; and a dosage of 2×10¹²/cm².

[0115] Then, a nickel acetate salt solution containing nickel of 10 ppmin weight is applied using a spinner. Instead of the application, amethod of spraying nickel elements to the entire surface by sputteringmay also be used. Then, heat treatment is conducted to performcrystallization, thereby forming a semiconductor film having acrystalline structure. A heating process using an electric furnace orirradiation of strong light may be conducted for this heat treatment. Incase of the heating process using an electric furnace, it may beconducted at 500 to 650° C. for 4 to 24 hours. Here, after the heatingprocess (500° C. for 1 hour) for dehydrogenation is conducted, theheating process (550° C. for 4 hours) for crystallization is conducted,thereby obtaining a silicon film having a crystalline structure. Notethat, although crystallization is performed by using the heating processusing a furnace, crystallization may be performed by means of a lampannealing apparatus. Next, after the oxide film on the surface of thesilicon film having a crystalline structure is removed by dilutehydrofluoric acid or the like, a process of introducing oxygen into thefilm is performed. In Embodiment 1, after forming a thin oxide film (ata thickness of 1-10 nm) with ozone water, laser light (excimer laserlight with a repetition frequency of 30 Hz and energy density of 452.5mJ/cm²) is irradiated in a nitrogen atmosphere. In accordance with theprocess of introducing oxygen, the oxygen concentration in thesemiconductor film which has a crystalline structure is assigned in arange of 5×10¹⁸/cm³-1×10²¹/cm³, desirably, higher than 2×10¹⁹/cm³.

[0116] Incidentally, excimer laser light-with a wavelength of 400 nm orless, or second harmonic wave or third harmonic wave of a YAG laser isused for the laser light. In any case, pulse laser light with arepetition frequency of approximately 10 to 1000 Hz is used, the pulselaser light is condensed to 100 to 500 mJ/cm² by an optical system, andirradiation is performed with an overlap ratio of 90 to 95%, whereby thesilicon film surface may be scanned. Excimer laser light is not limitedto a pulse oscillation one, a continuous oscillation one also can beused.

[0117] Next, after the oxide film formed by the said laser lightirradiation is removed by dilute hydrofluoric acid, laser lightirradiation is performed again in a nitrogen atmosphere or in a vacuum,thereby leveling the semiconductor film surface. In Embodiment 1, laserlight (excimer laser light with a repetition frequency of 30 Hz andenergy density of 501 mJ/cm²) is irradiated in a nitrogen atmosphere. Bymeasuring the leveled semiconductor film surface through AFM, Ra becomes2 nm or less, Rms becomes 2 nm or less, and P-V value of unevennessbecomes 50 nm or less.

[0118] Next, the surface is processed with ozone water for 120 seconds,thereby forming a barrier layer comprised of an oxide film with athickness of 1 to 5 nm in total.

[0119] Then, an amorphous silicon film containing an argon element,which becomes a gettering site, is formed on the barrier layer to have athickness of 150 nm by sputtering. The film deposition conditions withsputtering in this embodiment are: a film deposition pressure of 0.3 Pa;a gas (Ar) flow rate of 50 sccm; a film deposition power of 3 kW; and asubstrate temperature of 150° C. Note that under the above conditions,the atomic concentration Of the argon element contained in the amorphoussilicon film is 3×10²⁰/cm³ to 6×10²⁰/cm³, and the atomic concentrationof oxygen is 1×10¹⁹/cm³ to 3×10¹⁹/cm³. Thereafter, heat treatment at650° C. for 3 minutes is conducted using the lamp annealing apparatus toperform gettering.

[0120] Subsequently, the amorphous silicon film containing the argonelement, which is the gettering site, is selectively removed with thebarrier layer as an etching stopper, and then, the barrier layer isselectively removed by dilute hydrofluoric acid. Note that there is atendency that nickel is likely to move to a region with a high oxygenconcentration in gettering, and thus, it is desirable that the barrierlayer comprised of the oxide film is removed after gettering.

[0121] Moreover, although an example, in which the semiconductor filmcontaining argon is made as a gettering site and thereby the getteringis performed, is shown, in place of the semiconductor film containingargon, the semiconductor film containing phosphorus or boron may also beused. Further, other gettering methods may be used, a gettering site isformed by doping phosphorus or boron alternatively, thereby performing agettering by conducting a heating treatment, and a gettering may beperformed by conducting a heating treatment in halogen gas atmosphere.

[0122] Then, after a thin oxide film is formed from ozone water on thesurface of the obtained silicon film having a crystalline structure(also referred to as polysilicon film), a mask made of resist is formed,and an etching process is conducted thereto to obtain a desired shape,thereby forming the island-like semiconductor layers 102 to 106separated from one another. After the formation of the semiconductorlayers, the mask made of resist is removed.

[0123] Then, the oxide film is removed with the etchant containinghydrofluoric acid, and at the same time, the surface of the silicon filmis cleaned. Thereafter, an insulating film containing silicon as itsmain constituent, which becomes a gate insulating film 107, is formed.In this embodiment, a silicon oxynitride film (composition ratio:Si=32%, O=59%, N=7%, H=2%) is formed with a thickness of 115 nm byplasma CVD.

[0124] Next, as shown in FIG. 4A, on the gate insulating film 107, afirst conductive film 108 a with a thickness of 20 to 100 nm and asecond conductive film 108 b with a thickness of 100 to 400 nm areformed in lamination. In this embodiment, a 50 nm thick tantalum nitridefilm and a 370 nm thick tungsten film are sequentially laminated on thegate insulating film 107.

[0125] As a conductive material for forming the first conductive filmand the second conductive film, an element selected from the groupconsisting of Ta, W, Ti, Mo, Al and Cu, or an alloy material or compoundmaterial containing the above element as its main constituent isemployed. Further, a semiconductor film typified by a polycrystallinesilicon film doped with an impurity element such as phosphorous, or anAgPdCu alloy may be used as the first conductive film and the secondconductive film. Further, the present invention is not limited to atwo-layer structure. For example, a three-layer structure may be adoptedin which a 50 nm thick tungsten film, an alloy film of aluminum andsilicon (Al—Si) with a thickness of 500 nm, and a 30 nm thick titaniumnitride film are sequentially laminated. Moreover, in case of athree-layer structure, tungsten nitride may be used in place of tungstenof the first conductive film, an alloy film of aluminum and titanium(Al—Ti) may be used in place of the alloy film of aluminum and silicon(Al—Si) of the second conductive film, and a titanium film may be usedin place of the titanium nitride film of the third conductive film. Inaddition, a single layer structure may also be adopted.

[0126] Next, as shown in FIG. 4B, masks 110 to 115 are formed by anexposure step, and a first etching process for forming gate electrodesand wirings is performed. The first etching process is performed withfirst and second etching conditions. An ICP (inductively coupled plasma)etching method may be preferably used for the etching process. The ICPetching method is used, and the etching conditions (an electric energyapplied to a coil-shape electrode, an electric energy applied to anelectrode on a substrate side, a temperature of the electrode on thesubstrate side, and the like) are appropriately adjusted, whereby a filmcan be etched to have a desired taper shape. Note that chlorine-basedgases typified by Cl₂, BCl₃, SiCl₄, and CC1 ₄, fluorine-based gasestypified by CF₄, SF₆, and NF₃, and O₂ can be appropriately used asetching gases.

[0127] In this embodiment, RF (13.56 MHz) power of 150 W is applied alsoto the substrate (sample stage) to substantially apply a negativeself-bias voltage. With the first etching conditions, a W film is etchedto form an end portion of the first conductive layer into a taperedshape. Under the first etching conditions, an etching rate to W is200.39 nm/min, an etching rate to TaN is 80.32 nm/min, and a selectionratio of W to TaN is about 2.5. Further, with the first etchingconditions, a taper angle of W is approximately 26° Thereafter, thefirst etching conditions are changed to the second etching conditionswithout removing the masks 110 to 1-15 made of resist. CF₄ and Cl₂ areused as etching gases, the flow rate of the gases is set to 30/30 sccm,and RF (13.56 MHz) power of 500 W is applied to a coil-shape electrodewith a pressure of 1 Pa to generate plasma, thereby performing etchingfor about 30 seconds. RF (13.56 MHz) power of 20 W is also applied tothe substrate side (sample stage) to substantially apply a negativeself-bias voltage. Under the second etching conditions in which CF₄ andC1 ₂ are mixed, both the W film and the TaN film are etched at the samelevel. With the second etching conditions, an etching rate to W is 58.97nm/min, and an etching rate to TaN is 66.43 nm/min. Note that an etchingtime may be increased by 10 to 20% in order to conduct etching withoutremaining residue on the gate insulating film.

[0128] In the first etching process as described above, the shape of themask made of resist is made appropriate, whereby the end portion of thefirst conductive layer and the end portion of the second conductivelayer each have a tapered shape due to the effect of the bias voltageapplied to the substrate side. The angle of the tapered portion issufficiently set to 15 to 45°.

[0129] Thus, first shape conductive layers 117 to 121 composed of thefirst conductive layer and the second conductive layer (first conductivelayers 117 a to 122 a and second conductive layers 117 b to 122 b) areformed by the first etching process. The insulating film 107 thatbecomes the gate insulating film is etched by approximately 10 to 20 nm,and becomes a gate insulating film 116 in which regions which are notcovered by the first shape conductive layers 117 to 121 are thinned.

[0130] Next, a second etching process is conducted without removing themasks made of resist. Here, SF₆, C1 ₂ and O₂ are used as etching gases,the flow rate of the gases is set to 24/12/24 sccm, and RF (13.56 MHz)power of 700 W is applied to a coil-shape electrode with a pressure of1.3 Pa to generate plasma, thereby performing etching for 25 seconds. RF(13.56 MHz) power of 10 W is also applied to the substrate side (samplestage) to substantially apply a negative self-bias voltage. In thesecond etching process, an etching rate to W is 227.3 nm/min, an etchingrate to TaN is 32.1 nm/min, a selection ratio of W to TaN is 7.1, anetching rate to SiON that is the insulating film 116 is 33.7 nm/min, anda selection ratio of W to SiON is 6.83. In the case where SF₆ is used asthe etching gas, the selection ratio with respect to the insulating film116 is high as described above. Thus, reduction in the film thicknesscan be suppressed. In this embodiment, the film thickness of theinsulating film 116 is reduced by only about 8 nm.

[0131] By the second etching process, the taper angle of W becomes 70°.By the second etching process, second conductive layers 124 b to 129 bare formed. On the other hand, the first conductive layers are hardlyetched to become first conductive layers 124 a to 129 a. Note that thefirst conductive layers 124 a to 129 a have substantially the same sizeas the first conductive layers 117 a to 121 a. In actuality, the widthof the first conductive layer may be reduced by approximately 0.3 μm,namely, approximately 0.6 μm in the total line width in comparison withbefore the second etching process. However, there is almost no change insize of the first conductive layer.

[0132] Further, in the case where, instead of the two-layer structure,the three-layer structure is adopted in which a 50 nm thick tungstenfilm, an alloy film of aluminum and silicon (Al—Si) with a thickness of500 nm, and a 30 nm thick titanium nitride film are sequentiallylaminated, under the first etching conditions of the first etchingprocess in which: BCl₃, Cl₂ and O₂ are used as material gases; the flowrate of the gases is set to 65/10/5 (sccm); RF (13.56 MHz) power of 300W is applied to the substrate side (sample stage); and RF (13.56 MHz)power of 450 W is applied to a coil-shape electrode with a pressure of1.2 Pa to generate plasma, etching is performed for 117 seconds. As tothe second etching conditions of the first etching process, CF₄, Cl₂ andO₂ are used, the flow rate of the gases is set to 25/25/10 sccm, RF(13.56 MHz) power of 20 W is also applied to the substrate side (samplestage); and RF (13.56 MHz) power of 500 W is applied to a coil-shapeelectrode with a pressure of 1 Pa to generate plasma. With the aboveconditions, it is sufficient that etching is performed for about 30seconds. In the second etching process, BCl₃ and C1 ₂ are used, the flowrate of the gases are set to 20/60 sccm, RF (13.56 MHz) power of 100 Wis applied to the substrate side (sample stage), and RF (13.56 MHz)power of 600 W is applied to a coil-shape electrode with a pressure of1.2 Pa to generate plasma, thereby performing etching.

[0133] Next, the masks made of resist are removed, and then, a firstdoping process is conducted to obtain the state of FIG. 4D. The dopingprocess may be conducted by ion doping or ion implantation. Ion dopingis conducted with the conditions of a dosage of 1.5×10¹⁴ atoms/cm² andan accelerating voltage of 60 to 100 keV. As an impurity elementimparting n-type conductivity, phosphorous (P) or arsenic (As) istypically used. In this case, first conductive layers and secondconductive layers 124 to 128 become masks against the impurity elementimparting n-type conductivity, and first impurity regions 1130 to 134are formed in a self-aligning manner. The impurity element impartingn-type conductivity is added to the first impurity regions 130 to 134 ina concentration range of 1×10¹⁶ to 1×10¹⁷/cm³. Here, the region havingthe same concentration range as the first impurity region is also calledan n⁻⁻ region.

[0134] Note that although the first doping process is performed afterthe removal of the masks made of resist in this embodiment, the firstdoping process may be performed without removing the masks made ofresist.

[0135] Subsequently, as shown in FIG. 5A, masks 135 to 137 made ofresist are formed, and a second doping process is conducted. The mask135 is a mask for protecting a channel forming region and a peripherythereof of a semiconductor layer forming a p-channel TFT of a drivercircuit, the mask 136 is a mask for protecting a channel forming regionand a periphery thereof of a semiconductor layer forming one ofn-channel TFTs of the driver circuit, and the mask 137 is a mask forprotecting a channel forming region, a periphery thereof, and a storagecapacitor of a semiconductor layer forming a TFT of a pixel portion.

[0136] With the ion doping conditions in the second doping process: adosage of 1.5×10¹⁵ atoms/cm²; and an accelerating voltage of 60 to 100keV, phosphorous (P) is doped. Here, impurity regions are formed in therespective semiconductor layers in a self-aligning manner with thesecond conductive layer 124 b as masks. Of course, phosphorous is notadded to the regions covered by the masks 135 to 137. Thus, secondimpurity regions 138 to 140 and a third impurity region 142 are formed.The impurity element imparting n-type conductivity is added to thesecond impurity regions 138 to 140 in a concentration range of 1×10²⁰ to1×10²¹/cm³. Here, the region having the same concentration range as thesecond impurity region is also called an n⁺ region.

[0137] Further, the third impurity region is formed at a lowerconcentration than that in the second impurity region by the firstconductive layer, and is added with the impurity element impartingn-type conductivity in a concentration range of 1×10¹⁸ to 1×10¹⁹/cm³.Note that since doping is conducted by passing the portion of the firstconductive layer having a tapered shape, the third impurity region has aconcentration gradient in which an impurity concentration increasestoward the end portion of the tapered portion. Here, the region havingthe same concentration range as the third impurity region is called ann⁻ region. Furthermore, the regions covered by the masks 136 and 137 arenot added with the impurity element in the second doping process, andbecome first impurity regions 144 and 145.

[0138] Next, after the masks 135 to 137 made of resist are removed,masks 146 to 148 made of resist are newly formed, and a third dopingprocess is conducted as shown in FIG. 5B.

[0139] In the driver circuit, by the third doping process as describedabove, fourth impurity regions 149, 150 and fifth impurity regions 151,152 are formed in which an impurity element imparting p-typeconductivity is added to the semiconductor layer forming the p-channelTFT and to the semiconductor layer forming the storage capacitor.

[0140] Further, the impurity element imparting p-type conductivity isadded to the fourth impurity regions 149 and 150 in a concentrationrange of 1×10²° to 1×10²′/cm³. Note that, in the fourth impurity regions149, 150, phosphorous (P) has been added in the preceding step (n⁻region), but the impurity element imparting p-type conductivity is addedat a concentration that is 1.5 to 3 times as high as that ofphosphorous. Thus, the fourth impurity regions 149, 150 have a p-typeconductivity. Here, the region having the same concentration range asthe fourth impurity region is also called a p⁺ region.

[0141] Further, fifth impurity regions 151 and 152 are formed in regionsoverlapping the tapered portion of the second conductive layer 125 a,and are added with the impurity element imparting p-type conductivity ina concentration range of 1×10¹⁸ to 1×10²⁰/cm³. Here, the region havingthe same concentration range as the fifth impurity region is also calleda p⁻ region.

[0142] Through the above-described steps, the impurity regions havingn-type or p-type conductivity are formed in the respective semiconductorlayers. The conductive layers 124 to 127 become gate electrodes of aTFT. Further, the conductive layer 128 becomes one of electrodes, whichforms the storage capacitor in the pixel portion. Moreover, theconductive layer 129 forms a source wiring in the pixel portion.

[0143] Next, an insulating film (not shown) that covers substantiallythe entire surface is formed. In this embodiment, a 50 nm thick siliconoxide film is formed by plasma CVD. Of course, the insulating film isnot limited to a silicon oxide film, and other insulating filmscontaining silicon may be used in a single layer or a laminationstructure.

[0144] Then, a step of activating the impurity element added to therespective semiconductor layers is conducted. In this activation step, arapid thermal annealing (RTA) method using a lamp light source, a methodof irradiating light emitted from a YAG laser or excimer laser from theback surface, heat treatment using a furnace, or a combination thereofis employed.

[0145] Further, although an example in which the insulating film isformed before the activation is shown in this embodiment, a step offorming the insulating film may be conducted after the activation isconducted.

[0146] Next, a first interlayer insulating film l53 is formed of asilicon nitride film, and heat treatment (300 to 550° C. for 1 to 12hours) is performed, thereby conducting a step of hydrogenating thesemiconductor layers. (FIG. 5C) This step is a step of terminatingdangling bonds of the semiconductor layers by hydrogen contained in thefirst interlayer insulating film 153. The semiconductor layers can behydrogenated irrespective of the existence of an insulating film (notshown) formed of a silicon oxide film. Incidentally, in this embodiment,a material containing aluminum as its main constituent is used for thesecond conductive layer, and thus, it is important to apply the heatingprocess condition that the second conductive layer can withstand in thestep of hydrogenation. As another means for hydrogenation, plasmahydrogenation (using hydrogen excited by plasma) may be conducted.

[0147] Next, a second interlayer insulating film 154 is formed from anorganic insulating material on the first interlayer insulating film 153.In this embodiment, an acrylic resin film with a thickness of 1.6 μm isformed. Then, a contact hole that reaches the source wiring 129, contactholes that respectively reach the conductive layers 127 and 128, andcontact holes that reach the respective impurity regions are formed. Inthis embodiment, a plurality of etching processes are sequentiallyperformed. In this embodiment, the second interlayer insulting film isetched with the first interlayer insulating film as the etching stopper,the first interlayer insulating film is etched with the insulating film(not shown) as the etching stopper, and then, the insulating film (notshown) is etched.

[0148] Thereafter, wirings and pixel electrode are formed by using Al,Ti, Mo, W and the like. As the material of the electrodes and pixelelectrode, it is desirable to use a material excellent in reflectingproperty, such as a film containing Al or Ag as its main constituent ora lamination film of the above film. Thus, source electrodes or drainelectrodes 155 to 160, a gate wiring 162, a connection wiring 161, and apixel electrode 163 are formed.

[0149] As described above, a driver circuit 206 having an n-channel TFT201, a p-channel TFT 202, and an n-channel TFT 203 and a pixel portion207 having a pixel TFT 204 comprised of an n-channel TFT and a storagecapacitor 205 can be formed on the same substrate. (FIG. 6) In thisspecification, the above substrate is called an active matrix substratefor the sake of convenience. In the pixel portion 207, the pixel TFT 204(n-channel TFT); has a channel forming region 167, the first impurityregion (n⁻ region) 145 formed outside the conductive layer 127 formingthe gate electrode, and the second impurity region (n⁺ region) 140functioning as a source region. Further, in the semiconductor layerfunctioning as one of electrodes of the storage capacitor 205, thefourth impurity region 150 and the fifth impurity region 152 are formed.Note that the semiconductor layer surface functioning as one ofelectrodes of the storage capacitor 205 is leveled, concretely, the leakcurrent can be reduced and reliability can be improved by setting Ra to2 nm or less, Rms to 2 nm or less, and P-V value of unevenness to 50 nmor less. The storage capacitor 205 is constituted of the secondelectrode 128 and the semiconductor layers 150, 152, and 168 with theinsulating film (the same film as the gate insulating film) 116 asdielectric.

[0150] Further, in the driver circuit 206, the n-channel TFT 201 (firstn-channel TFT) has a channel forming region 164, the third impurityregion (n region) 142 that overlaps a part of the conductive layer 124forming the gate electrode through the insulating film, and the secondimpurity region (n⁺ region) 138 functioning as a source region or adrain region.

[0151] Further, in the driver circuit 206, the p-channel TFT 202 has achannel forming region 165, the fifth impurity region (p⁻ region) 151that overlaps a part of the conductive layer 125 forming the gateelectrode through the insulating film, and the fourth impurity region(p⁺ region) 149 functioning as a source region or a drain region;

[0152] Furthermore, in the driver circuit 206, the n-channel TFT 203(second n-channel TFT) has a channel forming region 166, the firstimpurity region (n⁻ region) 144 outside the conductive layer 126 formingthe gate electrode, and the second impurity region (n⁺ region) 139functioning as a source region or a drain region.

[0153] The above TFTs 201 to 203 are appropriately combined to form ashift resister circuit, a buffer circuit, a level shifter circuit, alatch circuit and the like, thereby forming the driver circuit 206. Forexample, in the case where a CMOS circuit is formed, the n-channel TFT201 and the p-channel TFT 202 may be complementarily connected to eachother.

[0154] In particular, the structure of the n-channel TFT 203 isappropriate for the buffer circuit having a high driving voltage withthe purpose of preventing deterioration due to a hot carrier effect.

[0155] Moreover, the structure of the n-channel TFT 201, which is a GOLDstructure, is appropriate for the circuit in which the reliability takestop priority. Further, an example of manufacturing the active matrixsubstrate for forming a reflection type display device is shown in thisembodiment. However, if the pixel electrode is formed of a transparentconductive film, a transmission type display device can be formedalthough the number of photomasks is increased by one.

[0156] Note that, in this specification, the “electrode” is a part ofthe “wiring” and indicates a point where electrical connection is madewith another wiring or a point where the wiring intersects with thesemiconductor layer. Therefore, for the sake of convenience of thedescription, the “wiring” and the “electrode” are separately used.However, the “wiring” is always included in the term “electrode”.

[0157] Embodiment 2

[0158] This embodiment describes a process of manufacturing an activematrix liquid crystal display device from the active matrix substratefabricated in Embodiment 1. The description is given with reference toFIG. 7.

[0159] After the active matrix substrate as illustrated in FIG. 6 isobtained in accordance with Embodiment 1, an alignment layer is formedon the active matrix substrate of FIG. 6 and subjected to rubbingtreatment. In this embodiment, before the alignment layer is formed, anorganic resin film such as an acrylic resin film is patterned to formcolumnar spacers in desired positions in order to keep the substratesapart. The columnar spacers may be replaced by spherical spacers sprayedonto the entire surface of the substrate.

[0160] A counter substrate is prepared next. The counter substrate has acolor filter in which colored layers and light-shielding layers arearranged with respect to the pixels. A light-shielding layer is alsoplaced in the driving circuit portion. A planarization film is formed tocover the color filter and the light-shielding layer. On theplanarization film, an opposite electrode is formed from a transparentconductive film in the pixel portion. An alignment layer is formed overthe entire surface of the counter substrate and is subjected to rubbingtreatment.

[0161] Then the counter substrate is bonded to the active matrixsubstrate on which the pixel portion and the driving circuits areformed, using a sealing member. The sealing member has filler mixedtherein and the filler, together with the columnar spacers, keeps thedistance between the two substrates while they are bonded. Thereafter aliquid crystal material is injected between the substrates and anencapsulant (not shown) is used to completely seal the substrates. Aknown liquid crystal material can be used. The active matrix liquidcrystal display device is thus completed. If necessary, the activematrix substrate or the counter substrate is cut into pieces of desiredshapes. The display device may be appropriately provided with apolarizing plate using a known technology. Then FPCs are attached to thesubstrate using a known technology.

[0162] The structure of the thus obtained liquid crystal module isdescribed with reference to the top view in FIG. 7.

[0163] A pixel portion 304 is placed in the center of an active matrixsubstrate 301. A source signal line driving circuit 302 for drivingsource signal lines is positioned above the pixel portion 304. Gatesignal line driving circuits 303 for driving gate signal lines areplaced to the left and right of the pixel portion 304. Although the gatesignal Iine driving circuits 303 are symmetrical with respect to thepixel portion in this embodiment, the liquid crystal module may haveonly one gate signal line driving circuit on one side of the pixelportion. Of the above two options, a designer can choose the arrangementthat suits better considering the substrate size or the like of theliquid crystal module. However, the symmetrical arrangement of the gatesignal line driving circuits shown in FIG. 7 is preferred in terms ofcircuit operation reliability, drivingefficiency, and the like.

[0164] Signals are inputted to the driving circuits from flexibleprinted circuits (FPC) 305. The FPCs 305 are press-fit through ananisotropic conductive film or the like after opening contact holes inthe interlayer insulating film and resin film and forming a connectionelectrode 309 so as to reach the wiring lines arranged in given placesof the substrate 301. The connection electrode is formed from ITO inthis embodiment.

[0165] A sealing agent 307 is applied to the substrate along itsperimeter surrounding the driving circuits and the pixel portion. Ancounter substrate 306 is bonded to the substrate 301 by the sealingagent 307 while a spacer 310 formed in advance on the active matrixsubstrate keeps the distance between the two substrates constant (thedistance between the substrate 301 and the counter substrate 306). Aliquid crystal element is injected through an area of the substrate thatis not coated with the sealing agent 307. The substrates are then sealedby an encapsulant 308. The liquid crystal module is completed throughthe above steps.

[0166] Although all of the driving circuits are formed on the substratein the example shown here, several ICs may be used for some of thedriving circuits.

[0167] Embodiment 3

[0168] Embodiment 1 shows an example of reflective display device inwhich a pixel electrode is formed from a reflective metal material.Shown in this embodiment is an example of transmissive display device inwhich a pixel electrode is formed from a light-transmitting conductivefilm.

[0169] The manufacture process up through the step of forming aninterlayer insulating film is identical with the process of Embodiment1, and the description thereof is omitted here. After the interlayerinsulating film is formed in accordance with Embodiment 1, a pixelelectrode 601 is formed from a light-transmitting conductive film.Examples of the light-transmitting conductive film include an ITO(indium tin oxide alloy) film, an indium oxide-zinc oxide alloy(In₂O₃—ZnO) film, a zinc oxide (ZnO) film, and the like.

[0170] Thereafter, contact holes are formed in an interlayer insulatingfilm 600. A connection electrode 602 overlapping the pixel electrode isformed next. The connection electrode 602 is connected to a drain regionthrough the contact hole. At the same time the connection electrode isformed, source electrodes or drain electrodes of other TFTs are formed.

[0171] Although all of the driving circuits are formed on the substratein the example shown here, several ICs may be used for some of thedriving circuits.

[0172] An active matrix substrate is completed as above. A liquidcrystal module is manufactured from this active matrix substrate inaccordance with Embodiment 2. The liquid crystal module is provided witha backlight 604 and a light guiding plate 605, and is covered with acover 606 to complete the active matrix liquid crystal display device ofwhich a partial sectional view is shown in FIG. 8. The cover is bondedto the liquid crystal module using an adhesive or an organic resin. Whenbonding the substrate to the counter substrate, the substrates may beframed so that the space between the frame and the substrates is filledwith an organic resin for bonding. Since the display device is oftransmissive type, the active matrix substrate and the counter substrateeach needs a polarizing plate 603 to be bonded.

[0173] Embodiment 4

[0174] Various modules (active matrix type liquid crystal module andactive matrix type EC module) can be completed by the driver circuit andthe pixel portion formed by implementing the present invention. That is,all of electronic equipments integrated with the modules thereof can becompleted.

[0175] As such electronic equipment, there are pointed out a videocamera, a digital camera, a head mount display (goggle type display), acar navigation system, a projector, a car stereo, a personal computer, aportable information terminal (mobile computer, cellular phone orelectronic book) and the like. Examples of these are shown in FIGS. 9 to11.

[0176]FIG. 9A shows a personal computer including a main body 2001, animage input portion 2002, a display portion 2003 and a keyboard 2004.

[0177]FIG. 9B shows a video camera including a main body 2101, adisplay-portion 2102, a voice input portion 2103, operation switches2104, a battery 2105 and an image receiving portion 2106.

[0178]FIG. 9C shows a mobile computer including a main body 2201, acamera portion 2202, an image receiving portion 2203, an operationswitch 2204 and a display portion 2205.

[0179]FIG. 9D shows a goggle type display including a main body 2301, adisplay portion 2302 and an arm portion 2303.

[0180]FIG. 9E shows a player using a record medium recorded withprograms (hereinafter, referred to as record medium) including a mainbody 2401, a display portion 2402, a speaker portion 2403, a recordmedium 2404 and an operation switch 2405. The player uses DVD (digitalVersatile Disc) or CD as the record medium and can enjoy music, enjoymovie and carry out game or Internet.

[0181]FIG. 9F shows a digital camera including a main body 2501, adisplay portion 2502, an eye contact portion 2503, operation switches2504 and an image receiving portion (not illustrated).

[0182]FIG. 10A shows a front type projector including a projectionequipment 2601 and a screen 2602. Embodiment 3 can be applied to theliquid crystal module 2808 forming a part of the projection equipment2601, and the general device can be completed then.

[0183]FIG. 10B shows a rear type projector including a main body 2701, aprojection equipment 2702, a mirror 2703 and a screen 2704. Embodiment 3can be applied to the liquid crystal module 2808 forming a part of theprojection equipment 2702, and the general device can be completed then.

[0184] Further, FIG. 10C is a view showing an example of a structure ofthe projection equipment 2601 and 2702 in FIG. 10A and FIG. 10B. Theprojection equipment 2601 or 2702 is constituted by a light sourceoptical system 2801, mirrors 2802, and 2804 through 2806, a dichroicmirror 2803, a prism 2807, a liquid crystal display equipment 2808, aphase difference plate 2809 and a projection optical system 2810. Theprojection optical system 2810 is constituted by an optical systemincluding a projection lens. Although this embodiment shows an exampleof three plates type, this embodiment is not particularly limitedthereto but may be of, for example, a single plate type. Further, personof executing this embodiment may pertinently provide an optical systemsuch as an optical lens, a film having a polarization function, a filmfor adjusting a phase difference or an IR film in an optical path shownby arrow marks in FIG. 10C.

[0185] Further, FIG. 10D is a view showing an example of a structure ofthe light source optical system 2801 in FIG. 10C. According to thisembodiment, the light source optical system 2801 is constituted by areflector 2811, a light source 2812, lens arrays 2813 and 2814, apolarization conversion element 2815 and a focusing lens 2816. Further,the light source optical system shown in FIG. 10D is only an example andthis example is not particularly limited thereto. For example, a personof executing this embodiment may pertinently provide an optical systemsuch as an optical lens, a film having a polarization function, a filmfor adjusting a phase difference or an IR film in the light sourceoptical system. However, according to the projectors shown in FIG. 10,there is shown a case of using a transmission type electro-opticaldevice and an example of applying a reflection type electro-opticaldevice is not illustrated.

[0186]FIG. 11A shows a cellular phone including a main body 2901, asound output portion 2902, a sound input portion 2903, a display portion2904, an operation switch 2905, an antenna 2906 and an image inputportion (CCD, image sensor or the like) 2907.

[0187]FIG. 11B shows a portable book (electronic book) including a mainbody 3001, display portions 3002 and 3003, a record medium 3004, anoperation switch 3005 and an antenna 3006.

[0188]FIG. 11C shows a display including a main body 3101, a supportbase 3102 and a display portion 3103.

[0189] In addition, the display shown in FIG. 11C is small and mediumtype or large type, for example, screen of the display sized 5 to 20inches. Moreover, it is preferable to mass-produce by executing amultiple pattern using a substrate sized 1×1 m to form such sizeddisplay section.

[0190] As has been described, the range of applying the presentinvention is extremely wide and is applicable to electronic equipment ofall the fields. The electronic equipment of the present invention can beimplemented by freely combined with the structures in Embodiments 1 to3.

[0191] In accordance with the present invention, a number of rod shapecrystal grain aggregates (domains) are formed in a semiconductor film 15having a crystalline structure. All of the crystal grains in a certaincrystal grain aggregate (domain) are considered to have the same crystalorientation, and the size of the aggregate of crystal grains (domain) isequal to or greater than approximately 1 μm, with large aggregateshaving a size of several tens of micrometers. A TFT having superior TFTcharacteristics, such as field effect mobility, can be obtained whenusing the semiconductor film 15 having this crystalline structure as anactive layer.

What is claimed is:
 1. A method of manufacturing a semiconductor device,comprising: a first step of forming a semiconductor film having anamorphous structure on an insulating surface; a second step of adding ametallic element to the semiconductor film having an amorphousstructure; a third step of heat-treating the semiconductor film havingan amorphous structure to form a semiconductor film having a crystallinestructure, and then removing an oxide film from the crystallinesemiconductor film surface; a fourth step of introducing oxygen into thesemiconductor film having a crystalline structure to make an oxygenconcentration within the film from 5×10¹⁸/cm³ to 1×10²¹/cm³; a fifthstep of removing an oxide film on the surface of the semiconductor filmhaving a crystalline structure; and a sixth step of irradiating laserlight under an inert gas atmosphere or in a vacuum to level the surfaceof the semiconductor film having a crystalline structure.
 2. A method ofmanufacturing a semiconductor device, comprising: a first step offorming a semiconductor film having an amorphous structure on aninsulating surface; a second step of adding a metallic element to thesemiconductor film having an amorphous structure; a third step ofheat-treating the semiconductor film having an amorphous structure toform a semiconductor film having a crystalline structure; a fourth stepof introducing oxygen into the semiconductor film having a crystallinestructure to make the oxygen concentration within the film from5×10¹⁸/cm³ to 1×10²¹/cm³; a fifth step of removing an oxide film on thesurface of the semiconductor film having a crystalline structure; and asixth step of irradiating laser light under an inert gas atmosphere orin a vacuum to level the surface of the semiconductor film having acrystalline structure.
 3. A method of manufacturing a semiconductordevice, comprising: a first step of forming a semiconductor film havingan amorphous structure on an insulating surface; a second step of addinga metallic element to the semiconductor film having an amorphousstructure; a third step of heat-treating the semiconductor film havingan amorphous structure to form a semiconductor film having a crystallinestructure, and then removing an oxide film from the crystallinesemiconductor film surface; a fourth step of introducing oxygen into thesemiconductor film having a crystalline structure to make the oxygenconcentration within the film from 5×10¹⁸/cm³ to 1×10²¹/cm³; a fifthstep of removing an oxide film on the surface of the semiconductor filmhaving a crystalline structure; a sixth step of irradiating laser lightunder an inert gas atmosphere or in a vacuum to level the surface of thesemiconductor film having a crystalline structure; and a seventh step ofgettering the metallic element to remove the metallic element from, orreduce the concentration of the metallic element within, thesemiconductor film having a crystalline structure.
 4. A method ofmanufacturing a semiconductor device according to claim 1, wherein aconcentration of oxygen within the semiconductor film having anamorphous structure and formed by the first step is less than5×10¹⁸/cm³.
 5. A method of manufacturing a semiconductor deviceaccording to claim 2, wherein a concentration of oxygen within thesemiconductor film having an amorphous structure and formed by the firststep is less than 5×10¹⁸/cm³.
 6. A method of manufacturing asemiconductor device according to claim 3, wherein a concentration ofoxygen within the semiconductor film having an amorphous structure andformed by the first step is less than 5×10¹⁸/cm³.
 7. A method ofmanufacturing a semiconductor device according to claim 1, wherein thefourth step is a step of irradiating laser light under an inert gasatmosphere, or in a vacuum, after oxidizing the semiconductor surfacehaving a crystallization structure by using ozone water, the laser lighthaving an energy density which is lower than the energy density of thelaser light used in the sixth step by 30 to 60 mJ/cm².
 8. A method ofmanufacturing a semiconductor device according to claim 2, wherein thefourth step is a step of irradiating laser light under an inert gasatmosphere, or in a vacuum, after oxidizing the semiconductor surfacehaving a crystallization structure by using ozone water, the laser lighthaving an energy density which is lower than the energy density of thelaser light used in the sixth step by 30 to 60 mJ/cm².
 9. A method ofmanufacturing a semiconductor device according to claim 3, wherein thefourth step is a step of irradiating laser light under an inert gasatmosphere, or in a vacuum, after oxidizing the semiconductor surfacehaving a crystallization structure by using ozone water, the laser lighthaving an energy density which is lower than the energy density of thelaser light used in the sixth step by 30 to 60 mJ/cm².
 10. A method ofmanufacturing a semiconductor device according to claim 1, wherein thefourth step is a step of irradiating laser light under an atmospherecontaining oxygen or water molecules, the laser light having an energydensity which is lower than the energy density of the laser light usedin the sixth step by 30 to 60 mJ/cm².
 11. A method of manufacturing asemiconductor device according to claim 2, wherein the fourth step is astep of irradiating laser light under an atmosphere containing oxygen orwater molecules, the laser light having an energy density which is lowerthan the energy density of the laser light used in the sixth step by 30to 60 mJ/cm².
 12. A method of manufacturing a semiconductor deviceaccording to claim 3, wherein the fourth step is a step of irradiatinglaser light under an atmosphere containing oxygen or water molecules,the laser light having an energy density which is lower than the energydensity of the laser light used in the sixth step by 30 to 60 mJ/cm².13. A method of manufacturing a semiconductor device according to claim1, wherein the fourth step is a step of irradiating laser light under aninert gas atmosphere, or in a vacuum, after adding oxygen by ion dopingor ion implantation so that the oxygen concentration within thesemiconductor film having a crystallization structure is from 5×10¹⁸/cm³to 1×10²¹/cm³, the laser light having an energy density which is lowerthan the energy density of the laser light used in the sixth step by 30to 60 mJ/cm².
 14. A method of manufacturing a semiconductor deviceaccording to claim 2, wherein the fourth step is a step of irradiatinglaser light under an inert gas atmosphere, or in a vacuum, after addingoxygen by ion doping or ion implantation so that the oxygenconcentration within the semiconductor film having a crystallizationstructure is from 5×10¹⁸/cm³ to 1×10²¹/cm³, the laser light having anenergy density which is lower than the energy density of the laser lightused in the sixth step by 30 to 60 mJ/cm².
 15. A method of manufacturinga semiconductor device according to claim 3, wherein the fourth step isa step of irradiating laser light under an inert gas atmosphere, or in avacuum, after adding oxygen by ion doping or ion implantation so thatthe oxygen concentration within the semiconductor film having acrystallization structure is from 5×10¹⁸/cm³ to 1×10²¹/cm³, the laserlight having an energy density which is lower than the energy density ofthe laser light used in the sixth step by 30 to 60 mJ/cm².
 16. A methodof manufacturing a semiconductor device according to claim 1, whereinthe metallic element in the above structure is a metallic element forpromoting crystallization of silicon, and is one element, or a pluralityof elements, selected from the group consisting of Fe, Ni, Co, Ru, Rh,Pd, Os, Ir, Pt, Cu, and Au.
 17. A method of manufacturing asemiconductor device according to claim 2, wherein the metallic elementin the above structure is a metallic element for promotingcrystallization of silicon, and is one element, or a plurality ofelements, selected from the group consisting of Fe, Ni, Co, Ru, Rh, Pd,Os, Ir, Pt, Cu, and Au.
 18. A method of manufacturing a semiconductordevice according to claim 3, wherein the metallic element in the abovestructure is a metallic element for promoting crystallization ofsilicon, and is one element, or a plurality of elements, selected fromthe group consisting of Fe, Ni, Co, Ru, Rh, Pd, Os, Ir, Pt, Cu, and Au.